Isoxazole derivatives of



Patented Nov. 4, 1947 ISOXAZOLE DERIVATIVES OF SULFANILAMIDE Heinz M. Wuest, Upper Montclair, and Max Hoffer, Nutley, N. .L,

asslgnors to Hofimann-La Roche, Inc., Nutley, N. J., a corporation of New Jersey No Drawing. Application July 11, 1944, Serial No. 544,342

Claims. (Cl. 260-2395) Our invention relates to new'isoxazole derivatives, and to processes for manufacturing them. These derivatives are the 5-sulfanilamido-isoxazoles of the general formula wherein R and R are lower alkyl and/or lower alkoxy alkyl groups.

As is well known, hundreds of sulfanilamides have been synthesized, investigated and described in th literature. Only a few of them have their well established place intherapy and all hitherto known sulfa drugs have marked disadvantages.

One disadvantage of these known sulfanilamides is that they are weak acids and form sodium salts which in aqueous solution react strongly alkaline, having pH ranges from 9-11 (New and Nonoflicial Remedies 1943, p. 187; Feinstone et al., C. A. 1941 1509; Ellingson, J. A. C. S. 1941, 2524). The strongly alkaline solutions cannot be sterilized by boiling or autoclaving as they are unstable under such conditions (see N. N. R. 1943, p. 187/189). They can only be injected intravenously and not intramuscularly, as they are highly irritating to the tissues; even on intravenous injection they tend to produce thrombosis of the veins.

Another disadvantage of the sulfa drugs is their insolubility or. very slight solubility "in aqueous solutions at the pH of the body fluids, especially of urine with pH 5.5-7. Their precipitation in the kidneys in form of crystals (consisting of the sulfa drugs themselves or their N -acetyl derivatives) causes much trouble and can lead to the most severe consequences; the medicalliterature quotes many cases of renal calculus formation, impairment of urinary excretion, fatal toxemia and uremia.

With the object in view of overcoming these serious disadvantages of known sulfa compounds, we have made the surprising discovery that the compounds illustrated by the general formula shown. above in which a disubstituted isoxazole ring is attached to the N -position of sulfanila- .mide possess relatively high acidity which is strong enough to enable these compounds to form water-soluble salts with bases, which salts possess neutral or nearly neutral reaction. Owing to this outstanding physico-chemical property and in contrast to all known sulfa compounds, the salts are therapeutical agents of greatly improved characteristics and can be injected without irritation, as we shall demonstrate further below.

Sulfanilamide derivatives with the isoxazole ring attached in 'N p0siti0n of the sulfanilamide molecule have already been described in literature. These compounds are different from those of the present invention, as they are substituted by the sulfanilamide radical in 4-position of the isoxazole ring; nothing has been reported on their chemotherapeutic properties or their therapeutic value. (Carlo Musante, Gazz. Chim. Ital. 71, 565, 1941.)

Also, one sulfanilyl derivative of 5-amino-isoxazole is k n o w n, namely, 5-sulfanilamido-3- methyl-isoxazole. This compound was first described by Backer and de Jonge (Rec. Tav. Chim. 61, 465, 1942) without any details on its chemotherapeutic activity. Later, Anderson, Faith, Marson, Winnek and Roblln (J. A. C. S. 64, 2903, 1942) synthesized the same compound and found some degree of bacteriostatic activity, but very little effect on experimental animal infections. Experiments made in our laboratories have confirmed these negative results.

We have discovered that the picture changes completely when both the 3- and 4- positions of the isoxazole ring of these sulfanilamide derivatives are replaced by an alkyl and/or corresponding alkoxy alkyl radical so that compounds of the above mentioned structural formula are obtained. These disubstituted derivatives have exhibited a high activity against experimental animal infections. Broad series of experiments have shown that their curative eflect on mice infected with hemolytic streptococci, pneumococci type 1, 2 and 3, meningococci and staphylococci is comparable to thebest sulfa drugs and surpasses them in some cases, especially with respect to meningococci andv pneumococci. Their acute and chronic toxicity is very low; daily injections in rabbits with 1.0 g./kg. for four weeks and chronic feeding of rats with normal diet containing 2% of 5- sulfanilamido-Zi, 4-d i m e t h y l-isoxazole for 8 wherein R and R stand for a lower alkyl group, such as methyl, ethyl, propyl, isopropyl, butyl. isobutyl and tart. butyl. and/or an alkoxy-substituted lower alkyl group such as methoxy-, ethoxy-, propyoxy-, methyl, ethyl; propyl;:- isopropyl, butyl, isobutyl or tertiary butyl radical with p-acetyl amino benzene sulfonylchloride and splitting of: the acetyl group from the thus obtained acetamino-benzene-sulfonylamino-isoxazole derivative, by a saponification process.

Instead of p-acetylamino benzene sulfonylchloride;p-nitrobenzene-sulfonylchloride can be used forthe condensation; in this case the result ing' nitro compounds have to be reduced to the corresponding amino compounds in the usual way.

The water-soluble salts of our new compounds to which we have referred above and which have a neutral or nearly neutral reaction are those se-- lected from the group consisting of the alkali metal. alkaline-earth metal and strong organic base salts. Sodium hydroxide, carbonate orbicarbonate can be used to form the sodium salt,

and the free compounds can be titrated as monobasic acids with n-alkali in 50% alcohol. Ampul solutions for injections can easily be obtained from the alkali metal salts of our new compounds having a pH from 7.2-7.4; these solutions are stable and can be sterilized by boiling or autoclaving'without decomposition. They do not show 30 'sulfa drugs or their acetyl derivatives depend-on the solubility in urine at diflerent pH. .fi-illlsan and 'Plummer have shown these solubilitieszfor 3 sulfa drugs with the pyrimidine nucleus (sul'fadiazine, 'sulfamerazine and sulfamethazine, Proc. Soc. Exp. Biol. Med. 53.142, 1943). It is obvious that only the solubilities at pH under 7 are relevantas-urine isin most cases acid.. We have determined the solubility of a characteristic member of our new compounds at various pH and compared with the'curves of Gilligan and Plummer. The superiority of 5-sulfanilamido-'3,4-dimethyl-isoxazole over the pyrimidine compounds is exhibited in a, very drastic manner: the solubilit at H5-7 issohi hthat ithe th comy p g M r e 60. 200 volnp'arts water and 100 parts crystallizedpound itself nor its acetyl derivative will be deposited in the kidneys.

The following examples illustrate our invn:

7 tion:

Example 1 112. parts of 3,4-dimethyl-5-amino-isoxazole were dissolved in a mixture of 100 vol. parts of pyridine and '100 vol. parts of acetone. The mixture is cooled with cold water and 240 parts pacetamino-benzene sultonic acid chloride are added in small portions under stirring at temperatures of below 30. The mixture is left standing --overnight at -30 and then the B-acetaminobenzene-sulfonylamino-3,4-dimethyl-isoxazole is precipitated by the addition of water, Recrystalequ. w.=309; found: C=50.33, H=4.87, N=13.22

equ. w. =309.

100 parts of the 5-acetamino-benzene-sulfonyl amino-3,4-dimethyl-isoxazole are boiled under reflux with 500 vol. parts 15-20% aqueous hydrochloric acid for -45 minutes until all is dissolved.-

500 parts crystallized sodium acetate are added isoxazole are converted to.

, 1o saponifyins reagents can be used.

. 4 and the liquid left cooling for crystallization. The sulfanllamido-3,4-dimethyl-isoxazole is sucked off. washed with water and dried. In the pure stat; it forms white prisms with the melting-point 3 i 5 Analysis: Calcd. for. CuHuNaOJS': C=-i9.4, 8:430, N=l5.7, equiv.-w.=287; found: C=49.54, H=5.00, N=l5.72. equiv. w.=26l.

Also, instead of the hydrochloric acid alkaline parts of acetamino-benzene-sulfonyl-amino-3,4-dimethylisoxazole are heatedmith 500 vol. parts 3N-so dium hydroxide solution on a steam bath for one hour. The solution furnished the 5-sulfanil- 5 amide-3,4-dimethyl-is'oxazole when acidified with acetic acid in very good yield;

The 3,4- dimethyl-5-amino-isoxazole used as a starting material'is preparedby reacting acetoproplonitrile with a hydroylamine salt under simultaneous neutralization of the acid, liberated during the reaction in hot aqueous, not too diluted, solution. It. crystallizes in beautiful white prisms from water and showsa M. P. of

Example 2 224 parts 5-amino-3A-dimethyl-isoxazole are dissolved in a mixture of vol. parts pyridine plus 160 vol. parts acetone and 370 parts p-nitrobenzene-.S-sulfonylchloride are gradually added under cooling. After having stood at room temperature for 10 hours water is added. An oil is precipitated "which soon solidifies by crystallization. The crystals are sucked of! and washed .withfw t r. .1- '1"he crude p-nitrobenzene-5-sul- '4 dimethyl isoxazole contains benzene-sulfonyl-amino-dimeth- .1207") and can be separated to its solubility in alkali. The obenz'enesulfonyl amino dimethyl and meltsf'at-ld'i".

0 isoxazoleieanb cry'stallized'from diluted alcohol dimethyljisoxazole are suspended in 200 vol. parts alcoholga'nd .l5otvolgparts concentrated hydro- 45 chlori'c acid and heated to 6040". 40 parts zinc dust are gradually added under stirring. When the vigorous reaction has ceased the mixture is still keptboiling under reflux: for, 30 minute and then filtered from some undlssolved zinc dust.

Example 3 v 126 part of 3-ethyl-4-methyl-5-amino-isoxazole-(J. Pract. Chem. 47, 128 (1893)) are converted to Sm-aoetamino-bemene-sulfonyl-am- 0 ino-3-ethyl-4-methylI isoxazole in analogy to Example 1. The compound forms white prisms of the M. P. 169".

Analysis: Calcd. for C14H11N3O4S:C=52.0, H=5.3, N=13.0; found: C=52.l9, H=5.45.

The saponificationmay be carried out with 18% hydrochloric acid or 3. N-sodiumhydroxide solution in analogy to Example 1. It furnishes the fi-sulfanilamido-3-ethyl-4-methyl-isoxazole whichmelts at 127.

70 Analysis? Calcd. for C12H15N30zS:C=51.2,

n=5.43, N=14.95; found: c=51.2a, 11:5.42.

. Etamble 4. [156 parts .,3-ethoxymethyl-4-methyl-5-aminoj- 40 partso'fthe p}nltrobenzen'e-sulfonyl-aminothe corresponding acetyl-sulfanilamid with 240 parts p-acetaminobenzene-sulfonic acid chloride in pyridine, acetone and the latter is saponified in analogy to: Example 1. The 5 sulfanilamino 3 ethoxymethyl-4-methyl-isoxazole thus obtained has a M. P. of 127. 7

Analysis: Calcd. for C1aH1'zO4NaS:C=50.2, H=5.46, N=13'.5; found: :49.95, H=5.27.

The 3-ethoxymethyl-4-methyl-5-amino isoxazole can be prepared in the following way: A mixture of 70 parts ethoxyethylacetate and 35 parts propionitrile are gradually added to a suspension of 11 parts sodium in 100 vol. parts benzene or ether. lution under evolution of hydrogen. The vessel is cooled with ice-water from the outside and a reflux condenser is used on .the top of the vessel. The reaction is usually terminated after -6 hours when all sodium has dissolved.

fully added, shaken, and the aqueous layer re-- moved. It contains the sodium compound of ethoxyacetyl-propionitrile formed according to the equation:

The solution is acidified with acetic acid, the oil which separates is taken up in ether, the ether layer is Washed with water and the ether is then distilled 01f, finally'in a vacuum. The residue forms a slight brown oil and is pure enough for' the formation of the 3-ethoxymethyl-4-methyl- 5-amino-isoxazole according to the equation:

30 parts of the crude ethoxyacetyl-propionitrile are heated with 18 parts hydroxylamine-hydrochloride in a mixture of 20 vol. parts alcohol and 5 vol, parts water under addition of 25 parts potassium acetate for 30 minutes at 80 under reflux, The reaction mixture is left to cool off and. then extracted with ethyl acetate. The extract is dried over sodium sulfate and the ethylacetate I distilled oil. The residue crystallizes after cooling and can be recrystallized from water. The 3 ethoxymethyl 4 methyl-S-amino isoxazole thus obtained forms white prisms or plates and melts at 69-70.

Analysis: Calcd. for C7H12O2Nz:C=53.8, H=7.7, N=l7.95; found: 0:53.98, H=7.61.

Example 5 In a similar way, the lithium salt of 5- (p-aminobenzene-sulfonyl) -amino-3,4-dimethyl isoxazole The sodium gradually goes in sothan in water.

which contain four 'mol water of crystallization Water is carecan be prepared. It dissolves even at 0 to more It crystallizes in large prisms and its solubility in water is over 20% at ll-5.

Example 7 If the sodium salt of Example 5 is dissolved in water and the aqueous solution shaken with an excess of 5-sulfanilamido-3,4-diamethyl-lsox- 2.2016, the pH of the solution changes from a little above pH 8 to pH 7.2. The solution is filtered and can be sterilized at 100 without changing'the properties.

In a similar way, a solution of the lithium salt of pH 7.2 to 7.4 can be prepared. Stable solutions which contain 20% or more of the sulfanilamide can also beprepared. Similar solutions with a. pH varying from 7-7.5 can be obtained from the preparations of Examples 3 and 4.

Example 8 If an aqueous suspension of 5-sulfanilamido- .3,4-dimethyl-isoxazole is heated with an excess of calcium carbonate and then filtered, a stable solution containing the calcium salt o1?v the sulfanilamide is obtained. It has similar properties of Example 7 solutions. Instead of the calcium carbonate, magnesium carbonate gives a stable solution containing the magnesium salt of the sulfanilamide. Similar solutions are obainable from the preparations of Examples 3 and 4.

Example 9 If an aqueous suspension of 5-sulfanilamido- 3,4-dimethyl isoxazole is treated with diethanolamine to a pH of 7.2 to 7.4, the compound dissolves and furnishes a stable solution containing the diethanolamine salt of the sulfanilamide. High concentrated stable solutions of the sulfanilamide showing a pH of 7.2 to 7.4 thus can be prepared. Similar solutions result if, instead of diethanolamine, other organic bases such as ethanolamine, ethylenediamine are used.

If instead of the 5-'sulfanilamido-3,4-dimethyl isoxazole the sulfanilamides from Examples 3 and 4 are used, solutions of the respective sulfanilamides showing analogy to the properties of the 5-sulfanilamido-3,4-dimethyl isoxazole are obtained.

What we claim is:

1. A compound selected from the group consisting of 5-sulfanilamido-3,4-dimethyleisoxazole, 5- sulfanilamido-3-oxymethy1-4 methyl isoxazole, and 5-sulfanilamldo-3-ethyl-4-methyl isoxazole, and alkali metal salts thereof.

' 2. A compound of the class consisting of 5-sulfanilamido-3,4-dimethyl-isoxazole of the formula CH3 CH3 4 3 NH SOs-NH-CS and alkali metal salts thereof.

4. The sodium salt of 5-sulfanliamido-3,4-dimethyl-isoxazole.

' 5. The lithium saitof 5-su1tan11amido-3A-di- Number Name j Date methyl-isoxazole. ,362,087 Newberry Nov. 7, 1944 mmz M. WUEST. 2,362,?36 Anderson Nov. 7. 1944 I a FOREIGN PA'I'ENTS REFERENCES CITED 1 Number Country Date 1 111,230 Australia Aug. 22 1940 The following references are of record in the A me of this patent: i 114,894 Australia Apr. 2,1942

UNITED STATES PATENTS OTHER REFERENCES Chemical Reviews, Aug, 1940. Pp. 105-109. Number Name Date JournaiAmer. Chem. Soc.. vol. 64, pp. 2902- 2,3 24,013 Moore July 13, 1943 2905 (Dec. 1942).

2.381. Hamilton Oct. 31, 1944 Chem.Abstracts,v0l.38,page232'1. 

